Ethylene-tetrafluoroethylene copolymers have good thermal, chemical, electrical and mechanical properties and are melt-processible. These copolymers are known to be heat-resistant thermoplastic resins which have a melting point of 260.degree. to 300.degree. C. However, the copolymers thermally deteriorate and become colored, brittle and foamed when heated to a temperature higher than the melting point for a long period of time. Accordingly, it is desirable to prevent the thermal deterioration of ethylene-tetrafluoroethylene copolymers during the conventional operation of injection molding and extrusion molding processes.
U.S. Pat. No. 4,110,308 discloses that a copper compound, such as metallic copper, cupric oxide or cuprous oxide, cupric nitrate, cupric chloride or copper alloys, stabilize the copolymers against degradation at elevated temperatures.